Proposed is a continuation of a study of the hormonal control of the commitment of the insect epidermal cell to either larval or pupal differentiation. Ecdysone in the absence of juvenile hormone either in vivo or in vitro changes the commitment of the larval epidermis to pupal; the addition of juvenile hormone prevents this change. Thus, this system can be used to study the biochemical events occurring during this permanent change in cellular commitment and also to learn more about the mode of the morphogenetic action of juvenile hormone. Since mRNA synthesis appears necessary to the ecdysone-induced change in commitment, the mRNA's produced will be isolated and their protein products assessed. The differences between RNA's produced in the presence of ecdysone and in the presence of JH will be compared. Both the cuticle proteins and the non-histone proteins will be studied for a clue to a protein product for these new mRNA's. The role of the non-histone proteins in the permanent change in commitment will also be assessed. Other studies will be concerned with the properties of the cellular receptors for juvenile hormone and their control by both juvenile hormone and ecdysone. Also, the biochemical events occurring during the ecdysone-induced change in commitment and the subsequent ecdysone-free period which are prerequisite for tanning of subsequently formed pupal cuticle will be explored.